1. Field of the Invention
This invention relates, in general, to railroad cars and, more specifically, to a cold formed center sill and its method of manufacture.
2. Summary of the Prior Art
The center sill is the primary structural member of the underframe of a railcar. It is subjected to the buff and draft forces created during operation of the railcar and normally extends as a continuous member along the length of the car body. In the past, center sills have possessed many different cross-sectional configurations depending on the type of railcar and other considerations. Center sills have been in the shape of hat designs, C-sections and other configurations. Regardless of its particular shape, it is well known to form a center sill by welding a plurality of hot rolled flat pieces or hot rolled sections together as a unit along its substantial length. The use of numerous welds to manufacture center sills presents several long-existing problems. Because numerous welds are needed, the reliance on this process to fabricate a finished center sill is inefficient from both a cost and productivity standpoint. The application of the welds along the lengths of the pieces being joined as a center sill is labor-intensive and cannot attain high-speed production. In addition, the application of multiple welds heats the material being joined and results in heat distortion and warpage. Warpage creates deviations in the straightness or acceptable tolerances of the center sill being formed. As a result, further physical steps are needed to finish the welded center sill unit and conform it to acceptable tolerances in camber, sweep and twist to be suitable for use in a railroad car. Existing center sills are subject to crippling of the webs which requires thicker cross sections at critical structural areas. Furthermore, hot rolled sections do not always result in the desired tolerances for the finished camber of the sill. As an additional important consideration, a welded center sill is an inherently heavy structure due to its design and fabrication technique. Accordingly, it is desirable in the prior art to provide an improved, lightweight center sill in which the necessity of a plurality of welds or other securement techniques are eliminated.